U.S. Pat. No. 4,429,990 granted to E. J. Tamary, Feb. 7, 1984 discloses a wicking structure for applying release liquid to the surface of a roller in a roller fixing apparatus. Release liquid, commonly referred to as "oil," is transported under pressure from a container to a permanent internal feed tube located inside a replaceable porous applicating wick. The feed tube and wick constitute a wicking or application roller which, when in contact with the fixing roller, is rotated by it while it "oils" the surface. This structure has many advantages including ease in articulation, efficient and rapid application of oil in response to an appropriate signal and quite low wear on the fixing roller surface.
The structure shown in that patent is commonly called a "rotating wick" and has been adopted commercially in a number of copiers. The release liquid is delivered to the wicking structure using a pump through a feed means to the permanent, rotatable feed tube. The feed tube is cylindrical and has small holes drilled or punched along its elongated side walls through which liquid can pass. The replaceable wick surrounds the feed tube. It is installed by being pulled over the free end of the feed tube. The replaceable wick is a porous structure which includes an inner ceramic porous material that is covered by a porous and heat-resistant fabric such as wool or a comparable synthetic fabric. Such a synthetic fabric is marketed by DuPont under the trademark Nomex.RTM. and is a well known capillary fabric which is resistant to heat and used for a variety of fusing roller wicks.
As mentioned above, these wicking structures have been successful commercially. However, maintenance is complicated by the cost associated with the replaceable portion of the wick and by occasional clogging of the holes in the feed tube which clogging is not necessarily cleared merely by replacing the wicking structure.